Compact and low-insertion-loss polarization beam-splitting multimode filter using pixelated waveguides.

A polarization beam-splitting multimode filter using pixelated waveguides has been presented and experimentally demonstrated in this paper. Finite difference time domain method and direct binary search optimization algorithm are employed to optimize pixelated waveguides to realize compact size, broad bandwidth, large extinction ratio, low insertion loss, and good polarization extinction ratio. Measurement results show that, in a wavelength range from 1520 to 1560 nm, for the fabricated device working at transverse-electric polarization, the measured insertion loss is less than 1.23 dB and extinction ratio is larger than 15.14 dB, while for transverse-magnetic polarization, the corresponding insertion loss lower than 0.74 dB and extinction ratio greater than 15.50 dB are realized. The measured polarization extinction ratio larger than 15.02 dB is achieved. The device's length is only 15.4 µm.

A Biocompatible Supercapacitor Diode with Enhanced Rectification Capability toward Ion/Electron-Coupling Logic Operations.

The main challenge faced by the forthcoming human-computer interaction is that biological systems and electronic devices adopt two different information carriers, i.e., ions and electrons, respectively. To bridge the gap between these two systems, developing ion/electron-coupling devices for logic operation is a feasible and effective approach. Accordingly, herein a supercapacitor-based ionic diode (CAPode) that takes electrochemically amorphized molybdenum oxide as the working electrode is developed. Benefiting from its unique size and charge dual ion-sieving effects, the molybdenum oxide electrode exhibits a record-high rectification ratio of 136, which is over 10 times higher than those of reported systems. It also delivers an ultrahigh specific capacitance of 448 F g⁻1 and an excellent cycling stability of up to 20 000 cycles, greatly outperforming those of previous works. These excellent rectification capability and electrochemical performances allow the as-built CAPode to work well in AND and OR logic gates, validating great potential in ion/electron-coupling logic operations. More attractively, the superior biocompatibilities of molybdenum oxide and relevant constituent materials enable the constructed CAPode to be applied as bioelectronics without regard to biosafety, paving a new way toward forthcoming human-computer interaction.

Accumulation characteristic of nitrogen in reservoirs during the ice-covered period under superimposed influence of ice and sediments: A case study of Biliuhe reservoir.

Reservoirs located in middle and high latitudes freeze for months in winter, where the accumulation characteristics of pollutants are changed by superimposed influence of salt exclusion from ice on the surface and pollution release from sediments at the bottom. Taking total nitrogen (TN) of Biliuhe reservoir in Northeast China as an example, we developed a model to simulate TN accumulation characteristics influenced by ice and sediments during the freezing period (NACISF), and quantified contributions of TN from ice and sediments. Model parameters of ice and sediments were determined by laboratory freeze-up simulation experiment and sediment release flux simulation experiment, and water quality data were obtained from field investigations. Results showed that the annual average amount of TN input during the ice-covered period from 2015 to 2020 was 220.77 t, the output was 400.11 t, and the accumulated amount was 589.52 t. TN excluded from ice and released from sediments contributed 8.12% and 7.17% of the total TN inputs in winter, respectively. Analysis showed that the TN excluded from ice was positively correlated with ice thickness and initial TN concentration. The maximum ice thickness of Biliuhe reservoir had a 13 year cyclic feature, and the proportion of TN excluded from ice to the total TN inputs in different periods ranged from 10.68% to 17.30% (mean 13.18%). Meanwhile, TN accumulated seasonally as summer > autumn > winter > spring. The TN exclusion effect in 2050 would be weakened when considering the combined effects of climate change and human activities, with a reduction of about 40.85% compared to the current. It is concluded that the NACISF model took into account the influences of both ice and sediments, which provided a detailed understanding of the accumulation characteristics of TN during freezing period, and had important reference significance for water quality management in winter.

Water Level Decline in a Reservoir: Implications for Water Quality Variation and Pollution Source Identification.

Continuous water-level decline makes the changes of water quality in reservoirs more complicated. This paper uses trend analyses, wavelet analysis and principal component analysis-multiple linear regression to explore the changes and pollution sources affecting water quality during a period of continuous reservoir water level decline (from 65.37 m to 54.15 m), taking the Biliuhe reservoir as an example. The results showed that the change of water level of Biliuhe reservoir has a significant 13-year periodicity. The unusual water quality changes during the low water level period were as follows: total nitrogen continued to decrease. And iron was lower than its historical level. pH, total phosphorus, and ammonia nitrogen were higher than historical levels and fluctuated seasonally. Permanganate index increased as water level decreased after initial fluctuations. Dissolved oxygen was characterized by high content in winter and relatively low content in summer. The pollutant sources of non-point source pollution (PC1), sediment and groundwater pollution (PC2), atmospheric and production & domestic sewage (PC3), other sources of pollution (PC4) were identified. The main source of DO, pH, TP, TN, NH4-N, Fe and CODMn were respectively PC3 (42.13%), PC1 (47.67%), PC3 (47.62%), PC1 (29.75%), PC2 (47.01%), PC1 (56.97%) and PC2 (50%). It is concluded that the continuous decline of water level has a significant impact on the changes and pollution sources affecting water quality. Detailed experiments focusing on sediment pollution release flux, and biological action will be explored next.

Seasonal Release Potential of Sediments in Reservoirs and its Impact on Water Quality Assessment.

Reservoir sediments act as important receivers and sources for nutrients in the overlaying water. To determine the sediments adsorption and release characteristics and their impacts on water quality, surface sediments samples collected from Biliuhe reservoir in August 2015 were studied through simulation experiments in a laboratory. The results demonstrated that the equilibrium concentrations (EC0) of ammonia nitrogen (NH4+-N) and total phosphorus (TP) were 8.29 mg/L and 0.025 mg/L, respectively, which were both higher than the average concentrations in the overlying water. Therefore, the sediments of Biliuhe reservoir mainly acted as the pollution sources for NH4+-N and TP, and the release to water showed a seasonal variation. When potential release amounts were considered, the average concentrations of NH4+-N and TP in the overlaying water could reach 6.4 mg/L and 0.21 mg/L, respectively, which significantly exceeded the current contents. Further, water quality exhibited a decreased tendency after taking the release potential of nutrients into account of water quality assessment. Among the samples, 42% and 33% of them in summer and autumn exceeded the third level of the National Surface Water Quality Standards of China (GB3838-2002). The results indicated that sediments release potential had an unignored influence on water quality during various seasons.

Effects of grazing exclusion on the grassland ecosystems of mountain meadows and temperate typical steppe in a mountain-basin system in Central Asia's arid regions, China.

Grazing exclusion has been proposed as a method of restoring degraded grassland ecosystems. However, its effectiveness remains poorly understood in mountain-basin grasslands in arid regions. Thus, we investigated the plant community characteristics, C and N storage levels, and soil organic carbon and total nitrogen concentrations and storage within the upper 0-40 cm soil layer in a grazed grassland (GG) and a fenced grassland (FG) with grazing exclusion in mountain meadow (MM) and temperate typical steppe (TTS) habitats in a mountain-basin ecosystem in an arid region of Central China, which are both vital grassland resources for livestock grazing and ecological conservation. In MM, our investigation revealed that grazing exclusion was beneficial to the productivity, coverage, height, diversity, and C and N storage of aboveground plants. However, grazing exclusion was not an effective option for soil C and N sequestration. In TTS, grazing exclusion effectively improved the plant productivity, coverage, height, plant and soil C and N sequestration, although it was not beneficial for maintaining plant diversity. Our findings suggest that reduced or rotational grazing may be a better choice than grazing exclusion in MM. In addition, considering the trade-off between biomass productivity and species diversity in TTS, short-term grazing exclusion should be considered. Additionally, grazing exclusion should be combined with other appropriate measures rather than operating on a standalone basis.